cabana: fix crash when combining graphs on MacOS (#27128)

old-commit-hash: ba5c6715a8

tools/cabana/chartswidget.cc

@@ -578,9 +578,10 @@ void ChartView::mousePressEvent(QMouseEvent *event) {
     if (dropAction == Qt::MoveAction) {
       return;
     }
-  }
+  } else {
     QChartView::mousePressEvent(event);
   }
+}
 
 void ChartView::mouseReleaseEvent(QMouseEvent *event) {
   auto rubber = findChild<QRubberBand *>();